There are some places that refer to the whole reg setup as an octopus, which was where the original name came from. The "octo" we know was always a "safe second (stage)" which was the cause of the octopus comments (remember this pre-dated SPG, the first reg sets had only one hose to a second stage. Adding a safe second made the whole thing look like an octopus, hence the confusing nomenclature).
To the OP, generally accepted usage on this board is that a "First Stage" is connected to a "Second Stage" by means of a "LP (low pressure) hose".
In addition a redundant second stage may be added, this is referred to either as an "octo" or "backup 2nd stage" depending who you ask.
Another LP hose will lead to a QD (quick disconnect) designed to fit onto the Low Pressure Inflator ("LPI") which is the bit with the buttons used to inflate or deflate your BC(D).
An "HP (high pressure) hose" will connect from the 1st stage to a pressure measuring device. This is either a SPG or a computer. Often the SPG / computer will have a "boot" which they fit into which often contains a depth gauge and / or a compass. This multi-instrument housing is referred to as a "console". Some computer manufacturers make a Personal Dive Computer (PDC) which does not read pressure but is shaped like a hockey puck to enable replacing the depth gauge in a normal console, or to be worn in a wrist mount. these puck-shaped computers are referred to as....wait for it...."Puck Computers".
None of this is meant to teach you anything, you already know this, it's more to just make sure we are all on the same page with regard to naming so that confusion is avoided.